Use root metadata only where supported

Root entries acquire _meta from MCP 2025-06-18. This is different from metadata on the surrounding roots result. Remove misplaced metadata or scope the containing example to protocol versions that define it.

Requirement

A root in a roots response may carry _meta from MCP 2025-06-18.

Details

Rule ID: mcp.root.meta.protocol-version
Owner: mcp
Surface: Root · Path: _meta
Kind: structural
Requirement level: must
Status: internal · Enforcement: internal

Protocol version applicability

2024-11-05	2025-03-26	2025-06-18	2025-11-25	2026-07-28
applies	applies	applies	applies	applies

Required by

• MCP Description 0.9.0, Sections 3.5, 3.6, and 9.4
  • 3. Document Structure: req-meta-protocol-version-availability
  • 9. Tools: req-interaction-protocol-version-valid

Based on

• Tier 1 — MCP schema.ts and normative specification text: MCP 2024-11-05 and 2025-03-26 schema.ts, interface Root (uri, name); MCP 2025-06-18 to 2026-07-28 schema.ts, interface Root (adds _meta)
  • validation/mcp-schemas/2024-11-05/schema.ts#L1041-L1059
  • validation/mcp-schemas/2025-03-26/schema.ts#L1182-L1200
  • validation/mcp-schemas/2025-06-18/schema.ts#L1415-L1440
  • validation/mcp-schemas/2025-11-25/schema.ts#L2111-L2136
  • validation/mcp-schemas/2026-07-28/schema.ts#L2746-L2775

Examples

Valid example

Source: expected-warning/open-step-responses-before-2026.json · Selected: /tools/0/interactionExamples/approved/steps/0/response/roots/0

{
  "uri": "file:///workspace/example",
  "_meta": {
    "trace": "root1"
  }
}

Invalid example

Source: expected-invalid/root-meta-before-2025-06-18.json · Selected: /tools/0/interactionExamples/with-root-meta/steps/0/response/roots/0

{
  "uri": "file:///workspace/example",
  "_meta": {
    "trace": "root1"
  }
}

Rule Source Code

result.yaml at immutable tag v0.9.0-rc.3.